[PATCH v3 10/24] dmaengine: dw-edma: Prepare LL kicks for event serialization

[Koichiro Den]

Both eDMA and HDMA perform the same remote LL read-back immediately
before writing the doorbell register.

A later patch serializes each LL doorbell write against IRQ event
capture with a raw spinlock. Keeping the read-back in the provider
callback would hold that lock across a remote read. Move the common
read-back into a core kick helper, where it can run before the
serialized section, and leave dw_edma_core_ch_maybe_doorbell() to decide
whether a kick is needed.

No functional change.

Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
Changes in v3:
  - New prep patch split from "Centralize LL doorbell decisions" to keep
    that policy change focused and the remote LL read-back outside the
    event lock added later. (Sashiko)

 drivers/dma/dw-edma/dw-edma-core.c    | 20 +++++++++++++++++++-
 drivers/dma/dw-edma/dw-edma-v0-core.c | 16 ----------------
 drivers/dma/dw-edma/dw-hdma-v0-core.c | 16 ----------------
 3 files changed, 19 insertions(+), 33 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index bb57f2d39d1c..e3d0559206d8 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -13,6 +13,7 @@
 #include <linux/dmaengine.h>
 #include <linux/err.h>
 #include <linux/interrupt.h>
+#include <linux/io.h>
 #include <linux/irq.h>
 #include <linux/dma/edma.h>
 #include <linux/dma-mapping.h>
@@ -254,6 +255,23 @@ static void dw_edma_finish_termination(struct dw_edma_chan *chan)
 	chan->status = EDMA_ST_IDLE;
 }
 
+static void dw_edma_core_ll_sync(struct dw_edma_chan *chan)
+{
+	/*
+	 * Remote controller registers and LL memory may be reached through
+	 * different paths. Complete posted LL writes before the doorbell.
+	 */
+	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
+		readl(chan->ll_region.vaddr.io);
+}
+
+/* Must be called with vc.lock held for an LL channel. */
+static void dw_edma_core_ch_kick(struct dw_edma_chan *chan)
+{
+	dw_edma_core_ll_sync(chan);
+	dw_edma_core_ch_doorbell(chan);
+}
+
 /* Must be called with vc.lock held. */
 static void dw_edma_core_ch_maybe_doorbell(struct dw_edma_chan *chan)
 {
@@ -261,7 +279,7 @@ static void dw_edma_core_ch_maybe_doorbell(struct dw_edma_chan *chan)
 	    chan->status != EDMA_ST_BUSY || !dw_edma_ll_pending(chan))
 		return;
 
-	dw_edma_core_ch_doorbell(chan);
+	dw_edma_core_ch_kick(chan);
 }
 
 static void dw_edma_device_caps(struct dma_chan *dchan,
diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
index d883ca446f5a..b3098eb83442 100644
--- a/drivers/dma/dw-edma/dw-edma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
@@ -480,20 +480,6 @@ static void dw_edma_v0_core_ch_enable(struct dw_edma_chan *chan)
 		  upper_32_bits(chan->ll_region.paddr));
 }
 
-static void dw_edma_v0_sync_ll_data(struct dw_edma_chan *chan)
-{
-	/*
-	 * In case of remote eDMA engine setup, the DW PCIe RP/EP internal
-	 * configuration registers and application memory are normally accessed
-	 * over different buses. Ensure LL-data reaches the memory before the
-	 * doorbell register is toggled by issuing the dummy-read from the remote
-	 * LL memory in a hope that the MRd TLP will return only after the
-	 * last MWr TLP is completed
-	 */
-	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
-		readl(chan->ll_region.vaddr.io);
-}
-
 static void dw_edma_v0_core_ch_config(struct dw_edma_chan *chan)
 {
 	struct dw_edma *dw = chan->dw;
@@ -624,8 +610,6 @@ static void dw_edma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
 {
 	struct dw_edma *dw = chan->dw;
 
-	dw_edma_v0_sync_ll_data(chan);
-
 	/* Doorbell */
 	SET_RW_32(dw, chan->dir, doorbell,
 		  FIELD_PREP(EDMA_V0_DOORBELL_CH_MASK, chan->id));
diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
index afc2f24fecd3..64a07fbc5be3 100644
--- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
@@ -282,20 +282,6 @@ static void dw_hdma_v0_core_ch_enable(struct dw_edma_chan *chan)
 		  HDMA_V0_CONSUMER_CYCLE_STAT | HDMA_V0_CONSUMER_CYCLE_BIT);
 }
 
-static void dw_hdma_v0_sync_ll_data(struct dw_edma_chan *chan)
-{
-	/*
-	 * In case of remote HDMA engine setup, the DW PCIe RP/EP internal
-	 * configuration registers and application memory are normally accessed
-	 * over different buses. Ensure LL-data reaches the memory before the
-	 * doorbell register is toggled by issuing the dummy-read from the remote
-	 * LL memory in a hope that the MRd TLP will return only after the
-	 * last MWr TLP is completed
-	 */
-	if (!(chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
-		readl(chan->ll_region.vaddr.io);
-}
-
 static void dw_hdma_v0_core_non_ll_start(struct dw_edma_chan *chan,
 					 struct dw_edma_burst *child)
 {
@@ -393,8 +379,6 @@ static void dw_hdma_v0_core_ch_doorbell(struct dw_edma_chan *chan)
 {
 	struct dw_edma *dw = chan->dw;
 
-	dw_hdma_v0_sync_ll_data(chan);
-
 	/* Doorbell */
 	SET_CH_32(dw, chan->dir, chan->id, doorbell, HDMA_V0_DOORBELL_START);
 }
-- 
2.51.0